In recent years, accompanying increases in communication capacity, optical communication systems using optical signals have come into wide use. Optical parallel transmission, by which data is transmitted/received using multiple channels, allows expansion of the data transmission bandwidth, leading to a broader range of applications of optical communication. However, such optical communication, which differs from transmission using electrical signals, tends to require a greater number of components for the transmission system. In addition, because optical components are less reliable than electrical components, communication failures are likely to occur more frequently in optical communication than in electrical transmission.
A server, etc., that processes data using an optical communication system operates on the assumption that the optical communication system continuously operates. For this reason, if a failure occurs in a certain channel of the optical communication system, it is impossible to immediately stop the optical communication system and replace a faulty optical component. To deal with the occurrence of failures, the optical communication system has to have redundancy so that operation can continue while maintaining a fixed transmission quality until the next maintenance period arrives.
Some methods of ensuring system redundancy in optical parallel transmission are known. For example, one method is to provide, in advance, a backup channel and when failure occurs, switch from the failing channel to the backup channel. Another method is to perform optical parallel transmission through multiple channels and when failure occurs, to transmit data for the failing channel through a channel operating normally (see, e.g., Japanese Laid-Open Patent Publication No. 2007-60494).
However, with the method mentioned first, a problem arises in that providing the backup channel used exclusively for a backup purpose and not used under normal situations results in increased initial construction cost. Furthermore, if the number of channels that fail exceed the number of the backup channels, a further problem arises in that the backup channel cannot accommodate data for the failed channels and thus, becomes incapable of data transmission. According to the method mentioned second, because all data for the failing channel is concentrated in the channels operating normally, the transmission band gets narrower as the number of failing channels increases.